In a drum type image reading scanner, an original is fixed on a surface of the drum of the image reading scanner and the image of the original is read by moving a reading head along the axis of the drum while the drum is rotated. In a drum type image recording scanner, a photosensitive film is fixed on a surface of the drum and an image is recorded on the photosensitive film by moving a recording head along the axis of the drum while the drum is rotated. That is, those drum type image reading scanner and drum type image recording scanner use similar drum scanning mechanisms.
For reading or recording an accurate image, it is important in these drum scanning mechanisms to securely fix the original sheet or the recording sheet on the drum and to prevent it from moving while the drum rotates.
Various sheet fixing mechanisms have been devised so far for that purpose. One is shown in the Publication of the Japanese Examined Utility Model Application No. S59-18778 in which, as shown in FIG. 6 of the Publication, an original 23 is inserted between a pair of transparent sheets 25 and 26 of a sheet holder 24, and the sheet holder 24 is fixed on the drum surface as shown in FIG. 7 of the Publication. For fixing the sheet holder 24 on the drum surface, a row of holes 29 and 30 are made at either end of the sheet holder 24, and a row of fixed pins 15 and a row of movable nails 18 corresponding to the holes 30 and 29 of the sheet holder 24 are formed on neighboring generatrix lines of the drum surface. By operating a lever 22 provided at an end of the drum, all the movable nails 18 sink down from the drum surface, and by releasing the lever 22, the movable nails 18 rise up on the drum surface. An original is fixed on the drum surface as follows. First the original 23 is inserted in the sheet holder 24. The holes 30 at one end of the sheet holder 24 are engaged with the fixed pins 15, and the sheet holder 24 is turned around the drum. While operating the lever 22, the other end of the sheet holder 24 is located over the sinking nails 18, and the lever 22 is released for raising the nails 18 to engage with the holes 29 of the other end.
In the above sheet fixing mechanism, one end and the other end of a sheet holder 24 engage with a row of fixed pins 15 and a row of movable nails 18, respectively. That is, two rows of engaging members must exist on the drum surface, which decreases the surface area of the drum that can hold an original (or a photosensitive film) and deteriorates the utility of the drum.